diff --git a/examples/grouping.php b/examples/grouping.php
new file mode 100644
index 0000000..0076315
--- /dev/null
+++ b/examples/grouping.php
@@ -0,0 +1,37 @@
+<?php
+
+include __DIR__ . "/../src/matrix.php";
+
+use divengine\matrix;
+
+// Create a matrix
+
+$table = new matrix([
+    ["Product", "Count"], 
+    //------------------
+    ["Apple",         2],
+    ["Banana",        3],
+    ["Banana",        5],
+    ["Orange",        6],
+    ["Orange",        5],
+    ["Orange",        2],
+    ["Orange",        3],
+]);
+
+// Show the matrix
+echo $table->formatTXT(true);
+
+// Group by
+$result = $table->groupBy([0], function($key, $group){
+    $sum = 0;
+    foreach($group as $row){
+        $sum += $row[1];
+    }
+    return [$key, $sum];
+}, true);
+
+echo "\n";
+$groupBy = new matrix(array_values($result));
+$groupBy->addRow(["Product", "Total"], onTop: true);
+echo $groupBy->formatTXT(true);
+
diff --git a/src/matrix.php b/src/matrix.php
index 9a3ef7f..c98a392 100644
--- a/src/matrix.php
+++ b/src/matrix.php
@@ -88,10 +88,6 @@ public function __construct(array $matrix)
      */
     public function validateMatrix(array $matrix): void
     {
-        if (empty($matrix) || !is_array($matrix[0]) || empty($matrix[0])) {
-            throw new InvalidArgumentException('Matrix must have at least one row with string headers');
-        }
-
         $numColumns = count($matrix[0]);
         foreach ($matrix as $row) {
             if (!is_array($row) || count($row) !== $numColumns) {